This invention relates to an electromagnetic shielding structure for covering a wire/cable or a wire harness, connected to I/O terminals of a motor on an electric car, or to I/O terminals of an ordinary electronic/electrical equipment so as to achieve the electromagnetic shielding thereof.
In recent years, weak-current circuits and electronic circuits have increasingly been used in automobiles, and installation wires have been formed into a large-current/high-voltage design, and under the circumstances it has been required to provide effective and inexpensive electromagnetic shielding means which protect the weak-current circuits (which can be easily affected by electromagnetic noises), and prevent the precision of detection by various sensors in the electronic circuits from being lowered by adverse effects of electromagnetic noises.
For example, in the case of a motor mounted on an electric car, it has been required to provide effective electromagnetic shielding means which prevent adverse effects of electromagnetic waves, generated from large-current/high-voltage power wire or cable, on external equipments, and prevent adverse effects of electromagnetic waves from the exterior.
In a structure shown in FIG. 4, a braided wire 14, formed by interweaving electrically-conductive metal wire elements into a tubular shape, is fitted on a bundle of wires 10 to cover the same, and this braided wire 14 is connected to a tubular metal shell 15 serving as a conductive shielding terminal, and the metal shell 15 is connected at its flange 15a to a mounting member, such for example as an outer casing B of a motor, by bolts 16. A distal end portion 14a of the braided wire 14 is press-fitted with an outer surface of the metal shell 15 over an entire periphery thereof by a fixing band 17 fastened by pressing to the distal end portion 14a. Metal terminals 13 are fastened by pressing respectively to conductors 11, exposed respectively at distal end portions of the wires 10, and the wire end portions, each having the metal terminal 13 connected thereto, are passed through a wire lead-in port b1 formed through the outer casing B, and the metal terminals 13 are connected to I/O terminals of the motor by respective bolts, thereby making electrical connection therebetween. In this case, the outer casing B is connected to the ground G, so that there is formed a shielding short-circuit path from the braided wire 14 to the ground G via the metal shell 15 and the outer casing B, thereby absorbing electromagnetic waves generated from the wires 10.
The braided wire 14 of the known type is formed by interweaving the above-mentioned metal wire elements, and there is another known type in which copper-plated strands are spirally wound on resin (e.g. polyester) strands to form meshwork wire elements, and these wire elements are interwoven into a tubular shape.
The braided wire 14, used in the electromagnetic shielding structure of FIG. 4, has the following problems.
In the manufacturing process, the long wires 10 are passed through the braided wire 14, and in this case the tubular braided wire 14, having a sufficiently large outer diameter, is used so that the insertion can be easily effected so as to enhance the efficiency of the operation. However, to use the braided wire 14 of a large diameter, having a length corresponding to the length of the wires 10, is costly, and therefore is disadvantageous.
In the case where the diameter of the braided wire 14 is thus sufficiently large, the plurality of wires 10 rub together within the braided wire upon vibration of a vehicle body, and therefore there is encountered a disadvantage that covering members 12 of the wires 10 are worn, so that the durability of the covering members 12 are adversely affected.
In connection with the above, in the case where a sufficient space is formed between the inner surface of the braided wire 14 and the wires 10, the non-conductive portions are liable to develop, so that the satisfactory electromagnetic shielding performance can not be obtained.
It is therefore an object of the invention to provide an electromagnetic shielding structure which can achieve a required shielding performance against electromagnetic waves generated particularly from installed large-current/high-voltage wires, and can meet variations in the size (such as a diameter) and number of wires of different kinds.
In order to achieve the above object, according to the present invention, there is provided a method of manufacturing an electromagnetic shielding structure for electric wires, comprising the steps of:
providing a bundle of electric wires having a first length and a first diameter;
providing a tubular braided wire having a second length which is shorter than the first length and a second diameter which is larger than the first diameter;
passing the bundle of electric wires through the braided wire;
connecting a connector to each of both ends of the electric wires collectively, the connector having a third diameter which is larger than the first diameter;
stretching the braided wire such that both ends thereof are fixed on the respective connectors to form a reduced-diameter portion therebetween which is fitted on an outer periphery of the bundle of the electric wire; and
attaching a conductive retainer on the reduced-diameter portion to maintain a length and a diameter of the reduced-diameter portion.
Preferably, the second length and the second diameter are determined such that the diameter of the reduced-diameter portion becomes substantially equal to the first diameter when the braided wire is stretched.
According to the present invention, there is also provided an electromagnetic shielding structure for electric wires, comprising:
a bundle of electric wires, having a first diameter;
a connector, collectively connected to each of both ends of the electric wires, the connector having a second diameter which larger than the first diameter;
a tubular braided wire, in which both ends thereof are fixed on the respective connectors to form a reduced-diameter portion therebetween which is fitted on an outer periphery of the bundle of electric wires; and
a conductive retainer, attached on the reduced-diameter portion to maintain a length and a diameter of the reduced-diameter portion.
In the above configurations, the operation for passing several wires through the short and wide braided wire is easy, and the braided wire can be used efficiently for several kinds of wires having different lengths and diameters, and the braided wire has the excellent general-purpose ability, and is economical. And besides, the non conductive portion of the braided wire relative to the electric wires hardly occurs, and the braided wire can absorb electromagnetic waves, generated from the wires, thereby achieving the satisfactory electromagnetic shielding performance. Furthermore, the inner surface of the braided wire is held in suitable contact with the electric wires, and therefore the wires will not rub together, and the durability of the wires against wear is enhanced.
Preferably, the retainer includes a tube member which is spirally wound on the reduced-diameter portion.
Alternatively, the retainer may include a pair of clip members which grips both end portions of the reduced-diameter portion.
Here, it is preferable that the clip members are connected by a rod member extending along the reduced-diameter portion.
In the above configurations, the outer diameter and the length of the reduced-diameter portion, formed by stretching the braided wire, can be easily maintained.